Steering clear of pomp and circumstance, Boeing Co. chose to fly quietly under the radar as it began moving into its new $750 million aircraft plant in North Charleston.

That milestone was technically reached Thursday, when Mayor Keith Summey handed company officials a certificate of occupancy covering part of the new 787 Dreamliner assembly line.

The informal ceremony at Boeing's Charleston International Airport campus capped an ambitious 18-month construction project that spawned a mammoth factory equivalent in size to roughly 12 football fields.

The first 200 of an estimated 3,800 employees who will work on the 787 project in North Charleston began settling into the new digs over the weekend. They included a mix of executives and support staff, Boeing Charleston spokeswoman Candy Eslinger said.

"People are excited about moving in. ... A good portion of those people were in different buildings off campus," she said Tuesday.

Eslinger said Boeing received a "temporary" certificate of occupancy because some areas of the plant are not yet completed. A ribbon-cutting ceremony is set for early June, with aircraft production to begin in July.

Boeing plans to deliver up to three of the new passenger jets a month from North Charleston by late 2013. "We're still on schedule," Eslinger said.

The 787 line is one of the largest single construction projects ever to spring from the ground in the Charleston area. Boeing broke ground on the 692,000-square-foot structure on Nov. 20, 2009, making North Charleston one of the few places in the world where wide-body commercial jets will be manufactured.

The construction team included BE&K/Turner Joint Venture and BRPH Architects-Engineers Inc., as well as numerous subcontractors.

The number of trade workers on the Boeing site peaked at about 2,400. Last week, the number totaled around 1,600. In all, they put in a total of 3.7 million man hours without a lost-time incident, said Mike Pace, BE&K/Turner's project director. In a statement, Pace called that "an amazing achievement."

Boeing officials have said the plant opening would not be affected by an April lawsuit filed by the National Labor Relations Board that seeks to relocate all 787 production to the Seattle area. The federal agency alleges the company built the line in union-averse South Carolina as an illegal form of retaliation against the International Association of Machinists and Aerospace Workers for previous strikes in Washington state.

Boeing has denied that and plans to contest the lawsuit. A hearing is set for June 14.